Piezoelectric crystals are well known in the art and are used for a number of purposes. Piezoelectric motors, transformers and linear drives are common. An important use for a piezoelectric crystal is in nebulisation. There are many cases where a fine mist of a substance is required without the application of heat. One example of this is a medical nebuliser, wherein a pharmaceutical compound is nebulised by a piezoelectric crystal in order to be inhaled by a patient. Another use for nebulisers is in the field of water dispersal such as garden water features. In order to disperse a dispersal agent effectively, a high voltage, high frequency drive source is required. Typically, a piezoelectric crystal for use in nebulisation is driven at its resonance frequency. This frequency varies between piezoelectric crystals, however it is usually in the region of 1.6-1.7 MHz.